1. Field of the Invention
This invention relates to the recovery of metallic copper from raw materials which contain chemically bound copper. More particularly, but not by way of limitation, the invention relates to the use of a metallic chloride leach solution for extracting copper values as soluble copper chloride salts from such raw materials, transforming the copper chloride solution to a copper sulfate solution by means of ion exchange, and then reducing the copper in the sulfate solution with a reducing gas to obtain high-grade metallic copper.
2. Brief Description of the Prior Art
A widely practiced method of recovering copper metal from copper-bearing ores is a smelting procedure by which high yields of good-grade, high-purity copper metal are obtained. When ores containing a significant sulfur content are smelted, however, much of the sulfur from the ore is discharged to the atmosphere as sulfur dioxide. For instance, one of the most abundant copper-containing minerals is chalcopyrite which contains copper in chemically combined form with iron and sulfur (CuFeS.sub.2). In the processing of this ore, about one ton of sulfur is produced for each ton of copper metal recovered. The recovery of this sulfur as liquid sulfur dioxide or as sulfuric acid is technically feasible, but large-scale production of these compounds will require nearby markets with sufficient capacity to absorb the production; otherwise, the economics of disposing of ths sulfur in these forms becomes unfavorable.
As a solution to this disposal problem, it has been proposed recently by Haver and Wong of the U.S. Bureau of Mines (Report of Investigation 7474, dated 1971) to leach copper ores containing sulfur with a ferric chloride solution and then recover elemental sulfur from the leach solution by filtration and solvent extraction. The leach solution containing the dissolved copper chloride values is passed to a cementation step where the metallic copper is recovered by conventional cementation. The removal of the sulfur from the leach solution and its ultimate recovery in elemental form has the advantage of yielding sulfur in a form which is more easily shipped and stored. A disadvantage of the Haver and Wong process, however, is that crushed sponge iron must be employed in order to obtain metallic (impure) copper.